Alpine touring bindings allow the heel of the user's footwear (such as a ski boot) to be latched to a snow travel aid (such as a ski), for sliding downhill (the “downhill mode”) and allow the heel to be released for walking and climbing (the “touring mode”). Release bindings allow the footwear to release from the snow travel aid when in the downhill mode, in case of a fall. When in the touring mode, the user may climb or walk with a great degree of freedom since the footwear is pivotally engaged with the aid near the toe of the footwear while the heel of the footwear is free to move upward and downward relative to the aid. A historical collection of such bindings can be viewed in the “Virtual Museum of Backcountry Skiing Bindings” at www.wildsnow.com, authored by Louis Dawson.
Alpine touring bindings sold under the brand DYNAFIT are release bindings that take advantage of the fact that modern alpine touring boots have a rigid sole. Thus, it is unnecessary to provide a bar, plate or other arrangement connecting the toe and heel units, as is the case with many other alpine touring bindings (see patent publications EP0199098, EP0519243, EP1559457, and AT402020).
The DYNAFIT™ binding system comprises a toe unit which has a set of jaws that pivotally engage a special insert in the footwear sole. The toe unit is mountable at an appropriate location on the upper surface of a snow travel aid. A separate heel unit is mountable at a particular region on the upper surface rearward of the toe unit, the location of which is dictated by the length of the footwear sole. The toe and heel units function independently in retaining the footwear attached to the snow travel aid. The heel unit comprises projections (typically a pair of pins) which extend forward to engage opposite sides of a fitting placed over a cavity in the rear of the footwear heel. Under forward release conditions, the pins are intended to be forced apart against spring pressure to respective release positions to disengage from the fitting and the heel. The pins communicate with a spring or springs through inclined sliding surfaces that move a block which engages the spring or springs at a central region of the block. This arrangement can result in forward release occurring when only one pin is displaced.
Fore and aft adjustment of the DYNAFIT™ heel unit to position the pins at an optimum depth in the heel fitting and to accommodate a limited range of different footwear sizes is provided by means of a threaded rod that moves a main portion of the heel unit relative to a base plate which is fixed to the upper surface of the snow travel aid. This is a fine adjustment that must be carried out by means of numerous rotations of the threaded rod, through the application of a tool such as a screwdriver or hex key.
The heel unit of a DYNAFIT™ binding provides lateral release primarily as a result of the body of the heel unit which contains the pins being pivotally engaged on a vertical post. Variable release settings are provided by adjusting compression of a spring that is internal to the body which forces a plunger against flattened portions arranged on the post circumference. There is a limited capacity for release values since the lateral and forward release components are all housed within the rotating body. In particular, the lateral release plunger is subjected to large and varying forces since it functions as part of a release mechanism and is also the means whereby the rotating component is retained on the base component.
To switch between touring and downhill modes with the DYNAFIT™ system, it is necessary to rotate the heel unit so that the pins either engage the footwear heel (downhill mode) or face away from the heel (touring mode). When the pins are facing away, the footwear heel is free to move upward and downward. A series of steps on the heel unit may also be provided which, upon rotation of the heel unit to different positions in the touring mode, allow the heel to be supported at varying heights above the snow travel aid to provide comfort during climbing. In order to switch from downhill mode to touring mode it is necessary to either forcibly release the pins from the fitting on the heel (not recommended) or disengage the toe unit from the footwear, so that the footwear completely exits from the binding system whereupon the heel unit may be rotated to a position in the touring mode. This can be difficult to do in deep snow or on steep slopes. Also, the DYNAFIT™ heel unit can rotate on its own while in the tour mode, occasionally causing the heel unit to inadvertently switch to the downhill mode.
The snow brake for the DYNAFIT™ binding is positioned to not contact snow while in the touring mode by the user forcing the heel plate of the brake downwards while simultaneously rotating the heel unit to a position in the touring mode. This requires a two-handed or other dual motion activity on the part of the user, which can be difficult to accomplish while in deep snow or when poised in a precarious location. Also, the brake unit may occasionally not deploy in a fall because the position of the heel unit in touring mode whereby the brake is restrained from deployment is very close to the position that the heel unit assumes during a lateral release.